Emilia is an emotionally battered wife. She is married to Iago, who does not treat her well. He is emotionally abusive to her, so Emilia lacks any real self confidence. Despite that, Emilia is the one who brings Iago down at the end of the play.
Despite her being in a terrible marriage with a rotten, plotting, power-hungry husband, she deeply wants to please him. When she says "I nothing but to please his fantasy," the reader can see that Emilia is still willing to go to great lengths to please her husband and his crazy fantasies. Emilia knows her husband's plans, and is actually willing to help for a while even. "Who would not make her husband a cuckold to make him a monarch? I should venture purgatory for't."
As for an actress to portray her, you would need to make sure the actress is not too young. Emilia has been married for some time and in that time she has been able to grow jaded toward love and marriage, despite her continued need to please Iago.
Julianne Moore or Nicole Kidman both have the acting ability to play a character that goes from battered and jaded to strong enough to defy her husband. They are both attractive enough still to make it look like someone as superficial and power-hungry as Iago would marry them. Courtney Cox might be able to pull it off, but I feel that she has been type cast as a comedic actress.